The present invention relates generally to the field of surface effect vessels. More particularly, the invention relates to a hull configuration and engine/blower arrangement for a high speed surface effect vessel that utilizes cushions of air to reduce friction between the boat hull and water surface.
Surface effect vessels which use cushions of air to reduce friction between the boat hull and the water are well known in the prior art. Basically, surface effect vessel technology involves injecting pressurized air under or between the hulls of a boat so that at least a portion of the boat""s hull rides upon a cushion of air. By utilizing gas pressure contained within a pocket under the hull, a surface effect vessel can operate at higher speeds and reduced power levels as compared to conventional vessels. This increased performance is due to the fact that the friction between the air cushion and the boat hull is substantially less than the friction between the water and the boat hull. Thus, riding upon a cushion of air allows a surface effect vessel to reach higher speeds and operate more efficiently with a smaller engine than a typical vessel.
There are many prior art designs which utilize this surface effect. For examples, see U.S. Pat. Nos. 5,860,380, 5,611,294, 5,415,120 and 5,176,095 to Burg, U.S. Pat. No. 5,570,650 to Harley, U.S. Pat. No. 4,574,724 to Stolper and U.S. Pat. No. 3,968,763 to Mason, the disclosures of which are hereby incorporated by reference. One of the primary problems with these and all other prior art designs is that the water/air seal that is maintained by the displacement of the hull allows excessive amounts of air to escape. This air loss increases the volume and pressure of the air required to maintain an air cushion under the vessel. Producing and providing pressurized air requires power from the vessel""s engines and blowers. Thus, the efficiency and performance of the vessel are greatly diminished when air escapes from the supporting air cushion.
Prior art surface effect vessels, such as those discussed above, further suffer from a number of other additional problems. For example, prior art surface effect vessels have a greater tendency to loose their supporting cushion of air in choppy or rough seas. As the surface effect vessel rolls in the rough seas, air in the supporting cushion tends to escape from the sides of the boat hull. In addition, air tends to escape from the supporting air cushion when the aft and bow portions of the surface effect vessel are lifted out of the water as the vessel pitches or rides over wave peaks. When air from the air cushion is lost, a larger portion of the vessel""s hull comes into contact with the water""s surface. This air loss results in dramatically increased friction between the vessel and the water and causes the vessel to slow down or lurch. Thus, maintaining the low friction air cushion beneath a vessel""s hull under adverse conditions is an important aspect of the design of surface effect vessels.
One prior art approach to maintaining the air cushion utilizes a flexible skirt positioned around the edges of the boat hull to help contain the air cushion. An example of such an embodiment is a hovercraft. Hovercraft are designed to vent air from their supporting air cushion in all directions. Surface effect ships typically utilize front and back flexible skirts with rigid side hulls. Unfortunately, the flexible skirts used in these types of applications increase the resistance of the vessel through contact with the water""s surface. Furthermore, the lifting air flows tend to escape from the skirts and be wasted when the hulls are lifted in high sea states. In addition, these flexible skirts require extensive and expensive maintenance. Furthermore, these skirts are still prone to allow more air to escape from the air cushion in rough seas.
Yet another problem with prior art surface effect vessels is that their hulls are substantially planar in the area in front of the air cavity. The hull is constructed to be planar in the region in front of the air cavity to allow the air cushion to extend as far as possible to the sides of the vessel. However, at high speeds or in rough seas, this planar hull section will tend to ride up on wave peaks. The bouncing of the vessel results in a rough bumpy ride and decreased stability. In addition, as the planar hull section rises and falls in the heavy seas, air tends to vent from the supporting air cushion. Therefore, what is needed is a surface effect vessel that is configured to operate in heavy seas.
V-shaped hulls are designed to provide an improved ride in rough water, as compared to relatively flat hulls, by deflecting wave energy away from and to the sides of the hull. Thus, traditional V-shaped hulls provide improved ride qualities at the expense of low speed planing and fuel efficiency. However, if the hull of a surface effect ship is made a moderate to deep V-shape, air from the air cushion tends to vent from the sides of the V-shaped hull when the vessel""s speed increases and the edges of the V-shaped hull rise out of the water. Thus, prior art surface effect vessels have not utilized deep-V hulls.
A preferred embodiment of the present invention is designed to address the above discussed problems with the prior art by providing an improved vessel for traveling over a water""s surface. The vessel includes a hull for supporting the vessel upon the water""s surface. The hull has at least one air cavity that is adapted to receive pressurized air from a blower. The blower has an air inlet that is positioned to face toward a bow of the vessel such that a pressure differential is generated whereby the blower generates an amount of forward thrust when air is sucked into the air inlet. The hull further includes a first air introduction means for introducing the pressurized air from the blower into the air cavity. Sealing side hull portions that are adapted to reduce air loss from the air cavity extend substantially parallel to the vessel""s direction of movement along the hull. Air lubricators provide a lubricating air flow along the sealing side hull portions and within the hull. A second air introduction means provides a sealing airflow of pressurized air to an edge of the at least one air cavity. The second air introduction means provides air at a higher velocity than the first air introduction means. In an especially preferred embodiment, the second air introduction means are boost ports that introduce air into the at least one air cavity near a bow side edge of the at least one air cavity such that an air flow is established wherein the air flows toward an aft portion of the vessel. The boost ports introduce air having a pressure at least 1.2 times as high as the first air introduction means. Movable sealing wedges prevent air from escaping from the air cavity. The sealing wedges are biased such that they substantially maintain contact with the water""s surface. The hull is configured such that, when the hull moves through air, air moving over the superstructure of the hull creates a low pressure zone above the superstructure of the hull such that the hull generates lift as the hull moves through the air.
The above discussed preferred embodiment of the present invention offers a number of substantial improvements over the prior art. For example, the supporting air cavity dramatically reduces the friction between the hull and the water""s surface. This friction is further reduced by the air lubricators that provide lubricating air flows to selected areas of the hull. The air cushion is efficiently maintained by the boost ports and the side hulls such that the pressurized air in the air cavities is substantially prevented from venting and causing the vessel to lurch. The lifting body effect created by the superstructure decreases the apparent weight of the vessel on the water""s surface thereby dramatically reducing the friction between the water and the lower portions of the hull. The pressure differential created by the forward placement and orientation of the blower inlet provides additional thrust to the vessel. Thus, the utilization of the multiple performance enhancing effects discussed above provides the vessel with increased range, speed and efficiency. Thus, the present invention is particularly useful for commercial applications such as high speed ferries and military applications such as patrol craft.
Another embodiment of the present invention provides a multi-hulled vessel that includes at least two asymmetric hulls such that an air tunnel is formed between the two hulls. A tunnel compression flap adjustably controls the amount of air that can flow through the air tunnel. The vessel further includes an air cavity beneath each of the at least two hulls wherein the air cavities receive pressurized air from a blower. The blower is positioned to utilize a ram air effect. Boost ports provide a high velocity sealing air flow to the air cavities such that a portion of the pressurized air in the air cavities is prevented from escaping. A fairing inlet port also supplies a sealing air flow. A surface drive prop propels the vessel. Air lubricators provide a lubricating air flow to at least a portion of the asymmetric hulls that is in contact with the water. The air lubricators have slotted grooves for transferring a portion of the pressurized air from the air cavities to portions of the hulls that are in contact with water. The slots are configured to provide a substantially uniform air flow. The vessel has a superstructure that is aerodynamically shaped to provide lift to the multi-hulled vessel when the multi-hulled vessel is moving by creating a low pressure zone above the superstructure.
The tunnel compression effect, ram air effect and lifting body effect of the above described embodiment combine to provide a surface effect vessel that has enhanced performance when compared to prior art designs. In particular, the tunnel compression effect acts in conjunction with the lifting body effect to provide lift that minimizes the friction between the vessel and the water""s surface. Furthermore, the ram air effect, provides addition thrust to the vessel without incurring any additional penalties in fuel consumption.
The present invention also encompasses a preferred method of constructing a surface effect vessel. In accordance with the preferred method, a lifting body configuration is utilized to provide aerodynamic lift when the vessel is in motion. The hull is further configured to utilize a tunnel compression effect. A surface effect means is utilized to provide pressurized air to at least one air cavity underneath the hull such that the pressurized air in the air cavity substantially prevents a portion of the hull from coming into contact with the water. The surface effect means is positioned on the vessel such that an air inlet of the surface effect means is oriented to utilize a ram air effect to generate an amount of forward thrust. A venturi effect is utilized to maintain air pressure in the air cavity. A control surface is provided to utilize air movement over the control surface to controllably produce either a lifting force or a downward force on the hull.
In yet another embodiment of the present invention, a boat is provided that has at least two asymmetric hull sections connected by an inner deck structure such that the inner deck structure is supported above the water""s surface to form an air tunnel between the two asymmetric hull sections. Air tunnel restricting means adjustably restrict the amount of air that can flow through the air tunnel thereby by inducing a tunnel compression effect. The boat includes a blower for providing pressurized air underneath the two hull sections such that a portion of the two hull sections is substantially prevented from coming into contact with the water""s surface. The blower has an inlet that is positioned such that air is forced into the inlet when the boat is moving in a forward direction. An air outlet damper and an air inlet damper controllably restrict the amount of air exiting and entering the blower. Water redirecting projections direct a flow of water toward a blow through area such that a portion of the pressurized gas is prevented from venting from underneath the asymmetric hulls through the blow through area. A venturi effect is utilized to draw air underneath the hulls. A surface drive prop provides thrust to propel the boat hull across the water""s surface. The surface drive prop has blades having a pitch that is controllably adjustable. An engine powers the blower and the surface drive prop. Coupling means couple the prop and the blower to the engine. The coupling means allow the prop to operate at a speed that is substantially independent of the speed of the engine. Air lubricators provide a lubricating air flow along portions of the two asymmetric hull sections. A non-trip side projection positioned on an exterior of each of the asymmetric hull portions exerts an upward force upon the associated asymmetric hull portion when the boat tips toward the non-trip side projection. Flow separators are positioned on the side hull portions such that the flow separators direct water away from the side hull portions.
The previously discussed embodiment of the present invention utilizes a number of friction reducing effects and features to improve the performance of a boat. In addition, the boat has features that allow the blower and the surface drive prop to be powered by the same engine. This is important because it is often desirable to have the blower provide a relatively constant air pressure while the prop is typically controlled with a throttle. In particular, the inlet and outlet dampers allow the speed of the blower to vary with the speed of the engine without a substantial change in the air pressure provided by the blower. Furthermore, the non-trip side projections allow the vessel to corner more tightly and improve the safety of the vessel by diminishing the likelihood of a rollover. Thus, this embodiment provides a number of distinct advantages over the prior art. While a number of embodiments have been described above, the embodiments are exemplary, not limiting, and it should be readily understood that the invention is susceptible to a variety of modifications and configurations. Therefore, having summarized various aspects of the invention in simplified form, the invention will now be described in greater detail with reference to the following figures wherein similar reference numerals designate similar features throughout the figures.